CN118007025A - Hot-rolled chromium-free low-strength high-plasticity spring steel wire rod and production process thereof - Google Patents
Hot-rolled chromium-free low-strength high-plasticity spring steel wire rod and production process thereof Download PDFInfo
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- 229910000639 Spring steel Inorganic materials 0.000 title claims abstract description 76
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 41
- 150000003839 salts Chemical class 0.000 claims abstract description 297
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 70
- 238000001816 cooling Methods 0.000 claims abstract description 56
- 238000005496 tempering Methods 0.000 claims abstract description 55
- 238000010791 quenching Methods 0.000 claims abstract description 52
- 230000000171 quenching effect Effects 0.000 claims abstract description 52
- 229910001562 pearlite Inorganic materials 0.000 claims abstract description 28
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 27
- 238000005098 hot rolling Methods 0.000 claims abstract description 22
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 20
- 230000009466 transformation Effects 0.000 claims abstract description 17
- 238000000034 method Methods 0.000 claims description 35
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- 229910052748 manganese Inorganic materials 0.000 claims description 5
- 238000009987 spinning Methods 0.000 abstract description 19
- 230000001105 regulatory effect Effects 0.000 abstract description 17
- 230000002159 abnormal effect Effects 0.000 abstract description 9
- 238000013461 design Methods 0.000 abstract description 9
- 238000005491 wire drawing Methods 0.000 abstract description 4
- 229910006639 Si—Mn Inorganic materials 0.000 abstract description 3
- 238000005096 rolling process Methods 0.000 description 20
- 229910000831 Steel Inorganic materials 0.000 description 15
- 239000010959 steel Substances 0.000 description 15
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- 229910052799 carbon Inorganic materials 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- 239000011572 manganese Substances 0.000 description 5
- 229910000734 martensite Inorganic materials 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 230000009467 reduction Effects 0.000 description 5
- 238000005299 abrasion Methods 0.000 description 4
- 230000009286 beneficial effect Effects 0.000 description 4
- 239000011651 chromium Substances 0.000 description 4
- 229910052710 silicon Inorganic materials 0.000 description 4
- 239000010703 silicon Substances 0.000 description 4
- 238000005728 strengthening Methods 0.000 description 4
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 3
- 230000002411 adverse Effects 0.000 description 3
- 238000004140 cleaning Methods 0.000 description 3
- 238000004806 packaging method and process Methods 0.000 description 3
- 239000006104 solid solution Substances 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 2
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- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
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Abstract
The invention relates to a hot-rolled chromium-free low-strength high-plasticity spring steel wire rod and a production process thereof, wherein the spring steel wire rod adopts a C-Si-Mn and chromium-free component design, the wire rod after hot rolling wire spinning is quenched into a mixed structure of bainite and residual austenite at the bainite transformation temperature in a first salt bath at a cooling rate of more than 30 ℃/s, then the temperature is raised and tempered in a second salt bath, the prepared structure comprises 10-20% by volume of tempered bainite, less than 20% by volume of ferrite and the rest pearlite, the quenching and tempering structure is regulated and controlled by utilizing the characteristic of high heat exchange capacity of molten salt, so that the wire rod strength-plasticity collocation is regulated, the chromium-free spring steel wire rod production of a low-strength high-plasticity non-abnormal structure is realized, the tensile strength Rm is 908-946 MPa, the section shrinkage Z is 63-68%, the risk of wire drawing broken wires in a wire manufacturing factory is effectively reduced, and the high-efficiency production of ultra-high-strength spring steel products is facilitated.
Description
Technical Field
The invention belongs to the technical field of alloy materials, and particularly relates to a hot-rolled chromium-free low-strength high-plasticity spring steel wire rod and a production process thereof.
Background
Along with the continuous development of the fields of automobiles, railways and engineering machinery, the application of the high-quality spring steel 55SiCrA capable of bearing high-cycle alternating load is continuously expanded under the light-weight development requirement. The existing ultrahigh-strength spring steel is mainly produced by high-quality spring steel 55SiCrA wire rods of various steel factories through drawing, oil quenching, tempering, spring winding and other procedures in wire drawing factories, and in order to further control the risk of wire breakage of the wire rods in the wire drawing factories, the refining specification of the steel wire finished products is reduced, the efficient production of the wire rods and the ultrahigh-strength spring steel finished products is realized, and the wire rod organization and the strong plasticity collocation are required to be regulated and controlled.
Technical difficulties and causes of the risk of drawing fracture of the spring steel wire rod in the prior art include:
(1) On one hand, the 55SiCrA wire rod steel adopts medium carbon content, cr is used as a medium-strength carbide forming element to improve the hardenability of the steel and obviously strengthen a matrix, but the coarsening risk of the carbide is increased to reduce the plasticity of the steel, and the risk of drawing broken wires is brought; on the other hand, in order to maintain the strength of the steel grade with the increase of the content of carbon or other alloy elements by adopting the means of reducing Cr content to improve the plasticity of the wire rod, and because the existing spring steel wire rod is subjected to cooling control through a stelmor air cooling line, for example, the spring steel wire rod with the deep-cooling drawing performance disclosed in the patent CN111041372B adopts a C-Si-Mn-controlled residual element component and a stelmor cooling process design, but because the stelmor air cooling line is insufficient in cooling control capacity, the cooling speed is about 10 ℃/s at most, and even if the cooling speed before phase transition is higher, only the spring steel wire rod taking sorbite as a main structure and a small amount of pearlite and ferrite as a microstructure can be obtained, so that the tensile strength is more than or equal to 1020MPa, the section shrinkage rate is more than or equal to 55%, and the drawing fracture is often caused by the fact that the matrix strength is high and the soft and hard phase drawing hardening is inconsistent in the drawing process of a wire drawing factory.
(2) On one hand, the stelmor wire-cooling and heat-preserving capability is limited, and after wire rods are spun, the stelmor wire-cooling is insufficient, so that abnormal structures such as martensite, bainite and the like appear in the cooling process of small-specification wire rods, the plasticity is obviously reduced, and the wire breakage phenomenon appears in the subsequent drawing process; on the other hand, in order to reduce risks of abnormal structures such as martensite and bainite and avoid the problems of overlong wire rod cooling on-line time and excessively low production rhythm and efficiency caused by overhigh coil collecting temperature, a stelmor air-cooled wire rod can adopt low-temperature wire-spinning at about 800 ℃, for example, the stelmor air-cooled wire-controlled cooling process for improving the structure and performance of a spring steel 55SiCrA wire rod disclosed in a patent CN106734261B adopts a low-temperature wire-spinning and air-cooled sectional air quantity control process design, but the low-temperature wire-spinning can lead to low rolling temperature of a rolling line before wire-spinning, high hardness of a rolling wire rod, increased requirement and abrasion of a rolling mill, and long wire rod cooling on-line time caused by heat preservation treatment, wherein the 55SiCrA wire rod structure consists of pearlite and a small amount of ferrite, the tensile strength of the material is up to 980-1060 MPa, the matrix strength is high, and the risk of drawing fracture is still easy to be aggravated.
(3) After wire rods are distributed on a roller way in a scattered manner, the two sides of the wire rods are piled up densely, the middle of the wire rods are thinned, so that corresponding tissues are obtained, when the cooling speed is increased by air cooling, the temperature difference exists between the wind receiving surface and the leeward surface of the wire rods, and the wire breakage rate is increased during processing due to uneven cooling speed and overhigh temperature difference in the lap joint area and the non-lap joint area of the wire rods, so that the same-circle strength difference of the wire rods is increased, and the excessive strength of the wire rods fluctuates.
Therefore, a chromium-free spring steel wire rod with low strength, high plasticity and no abnormal structure is lacking at present, so that the risk of wire breakage of the wire rod in drawing plants is controlled, and the high-efficiency production of wire rods and ultra-high strength spring steel finished products is realized.
Disclosure of Invention
The invention aims to solve at least one of the technical problems to a certain extent, and provides a hot-rolled chromium-free low-strength high-plasticity spring steel wire rod and a production process thereof, wherein the wire rod strength-plasticity collocation is regulated and controlled, so that the risk of drawing broken wires in a wire manufacturing plant is effectively reduced.
The technical scheme adopted for solving the technical problems is as follows:
the hot-rolled chromium-free low-strength high-plasticity spring steel wire rod comprises the following chemical components in percentage by mass: c:0.51% -0.59%, si:1.15 to 1.65 percent of Mn:0.55 to 0.85 percent, less than or equal to 0.020 percent of P, less than or equal to 0.015 percent of S, and the balance of Fe and unavoidable impurities; the structure of the spring steel wire rod comprises a mixed structure composed of 10-20% by volume of tempered bainite, less than 20% by volume of ferrite and the balance of pearlite.
The design basis of the chemical components and the mass percentages of the spring steel wire rod comprises:
(1) Carbon: carbon dissolves in steel to form solid solution, plays a role in gap solid solution strengthening, or combines with a strong carbide forming element to form carbide precipitation, plays a role in precipitation strengthening, and as the carbon content increases, the hardness and strength of the steel can be improved, but the plasticity can be reduced, and too high carbon content can cause too high matrix strength, embrittlement of the material and increase the drawing fracture risk, so that the mass percentage of C is controlled to be 0.51% -0.59%.
(2) Silicon: silicon is dissolved in ferrite to play a role in strengthening, so that the hardness and strength of steel can be improved, the silicon is also used as a deoxidizer and a reducing agent in the steelmaking process, but excessive silicon can cause overhigh strength and lower plasticity of a matrix and increase the drawing fracture risk, so that the mass percentage of Si is controlled to be 1.15-1.65%.
(2) Manganese: manganese can improve the hardenability of steel, has solid solution strengthening effect when being dissolved into a matrix, and can effectively improve the matrix strength, but too high manganese can aggravate segregation and grain growth risks, so that the mass percentage of Mn is controlled to be 0.55-0.85%.
(3) Phosphorus, sulfur: p and S are harmful elements in steel, which are unfavorable for the purity of the steel and can cause segregation, reduce the toughness of the steel and increase the brittleness, so that the mass percent of P is controlled to be less than or equal to 0.020 percent, and the mass percent of S is controlled to be less than or equal to 0.015 percent.
On the basis that the spring steel wire rod does not contain Cr, the strength of a matrix can be reduced, and the increase of the plasticity of the wire rod is facilitated, the tempered bainite in the microstructure has obviously increased strength compared with ferrite and pearlite, the tempered bainite accounting for 10% -20% of the volume percent can keep the wire rod to have certain matrix strength, the plasticity of the structure can be obviously improved compared with the bainite structure, the ferrite accounting for less than 20% keeps the wire rod to have certain plasticity, the pearlite has higher plasticity compared with ferrite, the mixed structure taking the pearlite as a main part enables the wire rod to have higher plasticity, the higher section shrinkage rate is represented, the wire rod can bear the drawing with higher reduction rate, the strength and the plasticity of the wire rod obtained by tissue regulation are low, and the wire rod obtained by tissue regulation can be further used for the application fields of manufacturing high-strength springs, and the like.
Preferably, the specification of the spring steel wire rod is 6-15mm, the tensile strength Rm is 908-946 MPa, the area reduction rate is 63-68%, and compared with a Steyr air-cooled wire rod, the spring steel wire rod has the characteristics of no chromium, low strength and high plasticity, and is beneficial to reducing the risk of wire breakage during drawing.
Preferably, the same-circle strength difference of the spring steel wire rod is less than or equal to 25MPa, and the spring steel wire rod has lower mechanical fluctuation than a stelmor air-cooled wire rod, thereby being beneficial to further reducing the risk of wire breakage during drawing.
A production process of a hot-rolled chromium-free low-strength high-plasticity spring steel wire rod is based on the chemical composition hot-rolling production wire rod of the hot-rolled chromium-free low-strength high-plasticity spring steel wire rod, wherein the wire rod is threaded into the wire rod, then passes through a first salt bath, the wire rod is quenched into a mixed structure of bainite and residual austenite at the bainite transformation temperature according to the cooling rate of more than 30 ℃/s, and then passes through a second salt bath for heating and tempering, so that the spring steel wire rod with the mixed structure composed of 10-20% by volume of tempered bainite, less than 20% by volume of ferrite and the balance pearlite is produced.
According to the production process, the wire rod subjected to hot rolling and wire spinning directly enters the first salt bath tank to be subjected to online salt bath, compared with the stelmor air cooling, the high heat exchange capacity of molten salt can be utilized, the cooling speed is obviously increased to be higher than 30 ℃/s, the wire rod is rapidly quenched at the bainite transformation temperature, part of austenite of a wire rod structure is transformed into bainite, part of residual austenite is reserved, the wire rod is subjected to salt bath heating tempering, bainite in the wire rod can be transformed into tempered bainite, the wire rod is kept to have certain matrix strength, the degradation effect of bainite as an abnormal hard and brittle phase structure on the plasticity of the wire rod is obviously improved, meanwhile, the residual austenite is transformed into ferrite and pearlite structure, the plasticity of the wire rod is effectively improved, the characteristics of components of the chromium-free spring steel are combined, the online rapid salt bath quenching and the salt bath isothermal tempering are designed, compared with the pearlite+ferrite structure obtained by stelmor air cooling the wire rod, the influence of chromium-free on the strength loss of steel grade is made up by a small amount of bainite, the influence of the abnormal structure of the bainite on the wire rod is properly reduced, and the influence of the wire rod on the disc is eliminated, the wire rod is caused by the wire rod is remarkably, the limit of chromium on the strength is eliminated, the wire rod has the hardness caused by the hard phase structure is obviously, and the soft phase structure is obviously has high, and has high hardness.
Preferably, the wire laying temperature of the wire laying process is more than 50 ℃ above the wire rod A3 point (the temperature at which the wire rod is completely converted into austenite), compared with the conventional stelmor wire rod which needs to be laid at a low temperature to reduce the risk of abnormal structures of martensite and bainite, the wire rod is rapidly cooled to the bainite transformation temperature through online salt bath quenching, preferably the cooling speed is 30-50 ℃/s, compared with the rapid cooling by air cooling, the required cooling time is less, the adverse effect of high Wen Tusi on the online time of controlled cooling is not considered, and the influence of bainite on the wire rod performance can be solved by high-temperature tempering, so that the rapid rolling in the hot rolling process can be realized by high Wen Tusi, and the abrasion on the rolling line in the hot rolling process can be reduced.
Preferably, the spinning temperature is 960-1000 ℃, so that rapid hot rolling and good preparation on a wire rod structure can be obtained.
Preferably, the salt bath quenching temperature of the first salt bath is 300-350 ℃, the salt bath quenching time is 25-35 s, the temperature of the bainite transformation nose tip of the wire rod under the steel grade is within +/-10 ℃ when the wire rod passes through the first salt bath, the lower the salt bath quenching temperature is, the longer the salt bath quenching time is, the more the bainite transformation is, the tempered bainite content is increased, the plasticity of the wire rod is reduced, and conversely, the higher the salt bath quenching temperature is, the higher the salt bath quenching time is, the lower the tempered bainite content is, the strength of the wire rod is reduced, the complete transformation of austenite into bainite is avoided, the lower the tempered bainite content is, the wire rod is quenched into a mixed structure of bainite and residual austenite by further controlling the salt bath quenching temperature and the salt bath quenching time, and the preparation on the structure is performed for salt bath tempering.
Preferably, the wire rod is rapidly cooled to the molten salt temperature in the first salt bath when passing through the first salt bath, so that the molten salt is heated, a salt heat exchanger can be used for rapidly exchanging heat and cooling the molten salt after quenching and heating, a group of molten salt circulating pumps are used for regulating and controlling the circulating quantity of the molten salt between the first salt bath and the salt heat exchanger, and the molten salt with the temperature of 300-350 ℃ is arranged in the first salt bath, preferably, the liquid level of the molten salt is maintained at 200-500 mm, and because the temperature drop range from high-temperature wire-spraying to salt bath quenching of the first salt bath is large, the circulating quantity of the molten salt in the first salt bath is 1000-1200 t/h, the temperature precision of salt bath quenching during continuous treatment can be controlled through the large circulating quantity of the molten salt, the temperature of the molten salt in the first salt bath is maintained to be less than or equal to 15 ℃, and the quenching transition is further precisely controlled.
Preferably, the salt bath tempering temperature of the second salt bath is 530-560 ℃, the salt bath tempering time is 300-380 s, the higher the salt bath tempering temperature is, the longer the salt bath tempering time is, the higher the content of residual austenite converted into pearlite is, the lower the ferrite content is, the higher the coil plasticity is, the lower the salt bath tempering temperature is, the shorter the salt bath tempering time is, the lower the pearlite content is, the higher the ferrite content is, the coil plasticity is reduced, the bainite structure is not fully converted, and the coil material is embrittled, so the coil structure conversion is further regulated and controlled by controlling the salt bath tempering temperature and the salt bath tempering time, and the quenching and tempering structure regulation of the spring steel coil is completed.
Preferably, the wire rod can be quickly heated to the molten salt temperature in the second salt bath when passing through the second salt bath, so that the molten salt is cooled, the second salt bath adopts circulating molten salt, preferably the molten salt liquid level is maintained at 200-400 mm, the molten salt after tempering and cooling can be quickly heat-exchanged and heated by adopting a salt heat exchanger, the molten salt circulation volume between the second salt bath and the salt heat exchanger is regulated and controlled by a group of molten salt circulation pumps, the molten salt temperature in the second salt bath is maintained to be less than or equal to 10 ℃, and further the tempering of the salt bath is accurately controlled.
Preferably, the wire rods are distributed on the roller way after spinning, and are sequentially conveyed along the first salt bath and the second salt bath through the roller way, so that the temperature difference of the lap joint area and the non-lap joint area of the wire rods is less than or equal to 10 ℃ through adjusting the roller way speed of the wire rods in the process of passing through the first salt bath and the second salt bath, and the same-circle strength difference of the wire rods can be further reduced.
Preferably, the initial roller speed of the second salt bath is higher than the end roller speed of the first salt bath, the roller speed of the coil rod is reduced after passing through the second salt bath for 20s, the positions of the lap joint area and the non-lap joint area on the coil rod of the loose coil are continuously adjusted through the speed change of the roller speed, so that the coil rod and molten salt exchange heat fully, and the temperature difference between the lap joint area and the non-lap joint area of the coil rod is effectively reduced.
Compared with the prior art, the invention has the beneficial effects that:
(1) Aiming at the problems that the existing hot rolled wire rod is high in matrix strength and low in plasticity of materials under the stelmor wire-controlled cooling process, and is easy to cause drawing fracture, the invention successfully develops the hot rolled low-chromium-free high-plasticity spring steel wire rod, adopts a chromium-free spring steel component design, has a microstructure type of a mixed structure consisting of tempered bainite, pearlite and ferrite, and can achieve the tensile strength Rm of 908-946 MPa and the reduction of area Z of 63-68% compared with an air-cooled wire rod by regulating and controlling the structure and strength of the hot rolled wire rod, so that the wire rod is low in strength and high in plasticity, is used for the application fields of manufacturing high-strength springs and the like, is beneficial to effectively reducing the drawing and breakage risk of wire mills, and realizes the efficient production of ultrahigh-strength spring steel finished products.
(2) The production process adopts the component design of the chromium-free spring steel, and combines the online rapid salt bath quenching and salt bath tempering isothermal technical process design, the salt bath has obviously improved cooling capacity compared with air cooling, the wire rod after spinning directly enters the salt bath and is rapidly quenched at the bainite transformation temperature, so that the austenite part is transformed into bainite, and then the bainite+residual austenite is transformed into tempered bainite+ferrite+pearlite by the high-temperature tempering of the salt bath, thereby completing the quenching and tempering structure regulation of the spring steel wire rod and controlling, and the chromium-free spring steel wire rod with low strength, high plasticity and no abnormal structure (martensite, bainite and the like) can be obtained; meanwhile, as the molten salt has the characteristic of high heat exchange capability, the temperature of the wire rod above A3 can be quickly reduced to the bainite transformation temperature, and compared with an air cooling line, the adverse effect of Wen Tusi on the structure and the on-line time is not required to be considered, so that the abrasion of a rolling line during hot rolling can be further reduced by adopting Wen Tusi.
(3) According to the production process, the temperature difference between the lap joint area and the non-lap joint area of the wire rod is adjusted by adjusting the roller speed of the wire rod passing through the first salt bath and the second salt bath, so that the same-circle strength difference of the wire rod can be further reduced, the same-circle strength difference is less than or equal to 25MPa, and the wire rod has lower mechanical fluctuation compared with a Steyr air-cooled wire rod, and the risk of wire breakage during drawing is further reduced.
Drawings
The foregoing and/or additional aspects and advantages of the invention will become apparent and may be better understood from the following description of embodiments taken in conjunction with the accompanying drawings in which:
Fig. 1 is a metallographic structure diagram of a wire rod of example 1 of the present invention which is a tempered bainite+ferrite+pearlite mixed structure;
FIG. 2 is a metallographic structure diagram of a wire rod of comparative example 1 of the present invention having a mixed structure of pearlite and bainite;
FIG. 3 is a metallographic structure diagram of a wire rod of example 2 of the present invention which is a tempered bainite+ferrite+pearlite mixed structure;
fig. 4 is a metallographic structure diagram of a wire rod of example 3 of the present invention which is a tempered bainite+ferrite+pearlite mixed structure.
Detailed Description
The embodiments described below are exemplary only and are not intended to limit the description of the features and characteristics of the invention, in order to set forth the best mode of carrying out the invention, intended to illustrate it and to enable those skilled in the art to practice it, without any limitation to its scope, which is defined solely by the claims appended hereto.
Example 1:
The invention relates to a production process of a hot-rolled chromium-free low-strength high-plasticity spring steel wire rod, which comprises the following chemical components in percentage by mass: c:0.51%, si:1.45%, mn:0.83%, P:0.008%, S:0.012%, the balance being Fe and unavoidable impurities; the production process comprises the steps of hot rolling, spinning, on-line salt bath quenching and on-line salt bath tempering, and specifically comprises the following steps of:
The hot rolling process is used for rolling square billets with the chemical components and the specification of 160mm multiplied by 160mm into wires with the diameter of 8mm through a rolling line, the wire laying process is used for rolling the wires subjected to hot rolling into wire rods through a wire laying machine, the wire laying temperature is controlled to be 975 ℃, the wire rods subjected to wire laying are distributed on a roller way in a scattered manner, and the wire rods are sequentially conveyed along a first salt bath and a second salt bath through the roller way.
The online salt bath quenching process is used for quickly reducing the temperature of the wire rod to the molten salt temperature according to the cooling speed of 41 ℃/s when the wire rod passes through the first salt bath after spinning, namely, the salt bath quenching temperature is controlled to be 302 ℃, the salt bath quenching time is controlled to be 34s, the quenched and warmed molten salt is quickly subjected to heat exchange and cooling by adopting a salt heat exchanger, the molten salt circulation quantity between the first salt bath and the salt heat exchanger is regulated and controlled by a group of molten salt circulation pumps, the molten salt liquid level of the first salt bath is maintained to be 200-500 mm, the molten salt circulation quantity of the first salt bath is 1150t/h, the molten salt temperature rise in the first salt bath is maintained to be less than or equal to 15 ℃, the end roller way speed of the first salt bath is 0.3m/s, and the wire rod is quenched to be a mixed structure of bainite and residual austenite at the bainite transformation temperature.
The second salt bath tank is internally provided with 534 ℃ molten salt, the online salt bath tempering procedure is used for quickly heating the wire rod subjected to online salt bath quenching to the molten salt temperature for high-temperature tempering when the wire rod is subjected to the second salt bath tank, namely, the salt bath tempering temperature is controlled to be 534 ℃, the salt bath tempering time is controlled to be 305s, the quenched and heated molten salt is quickly subjected to heat exchange and cooling by adopting a salt heat exchanger, a group of molten salt circulating pumps are used for regulating and controlling the circulating amount of the molten salt between the second salt bath tank and the salt heat exchanger, the liquid level of the molten salt in the second salt bath tank is maintained to be 200-400 mm, maintaining the temperature rise of molten salt in the second salt bath at less than or equal to 10 ℃, increasing the initial roller way speed of the second salt bath to 0.8m/s, reducing the roller way speed of the wire rod to 0.3m/s after the wire rod passes through the second salt bath for 20s, adjusting the temperature difference between the lap joint area and the non-lap joint area of the wire rod to less than or equal to 10 ℃, converting bainite in the wire rod into tempered bainite, converting residual austenite into ferrite and pearlite structures, cleaning, air cooling and collecting the wire rod discharged from the second salt bath, and then carrying out off-line transportation, packaging and warehousing to obtain a finished spring steel wire rod, wherein the metallographic structure diagram of the finished spring steel wire rod is shown in figure 1.
Comparative example 1:
The production process of the spring steel wire rod is different from the embodiment 1 in that: the production process comprises the following steps of hot rolling, spinning and stelmor air cooling line production, and specifically:
the coil rod after the stelmor wire spinning is controlled by the stelmor wire cooling line, the temperature is reduced by air cooling at the cooling speed of 10.1 ℃/s, then the coil rod enters a heat insulation cover, the cover entering temperature is 660 ℃, the phase change is completed in the cover at the cooling speed of 1.2 ℃/s, the spring steel coil rod is obtained after coil collection and coil discharging, and the metallographic structure diagram of the spring steel coil rod is shown in figure 2.
Example 2:
The invention relates to a production process of a hot-rolled chromium-free low-strength high-plasticity spring steel wire rod, which comprises the following chemical components in percentage by mass: c:0.54%, si:1.52%, mn:0.76%, P:0.01%, S:0.011%, the balance being Fe and unavoidable impurities; the production process comprises the steps of hot rolling, spinning, on-line salt bath quenching and on-line salt bath tempering, and specifically comprises the following steps of:
The hot rolling process is used for rolling square billets with the chemical components and the specification of 160mm multiplied by 160mm into wires with the diameter of 10mm through a rolling line, the wire laying process is used for rolling the wires subjected to hot rolling into wire rods through a wire laying machine, the wire laying temperature is controlled to be 985 ℃, the wire rods subjected to wire laying are distributed on a roller way in a scattered manner, and the wire rods are sequentially conveyed along a first salt bath and a second salt bath through the roller way.
The online salt bath quenching process is used for quickly reducing the temperature of the wire rod to be the molten salt temperature according to the cooling speed of 38 ℃/s when the wire rod passes through the first salt bath after spinning, namely, the salt bath quenching temperature is controlled to be 315 ℃, the salt bath quenching time is controlled to be 30s, the quenched and warmed molten salt is quickly subjected to heat exchange and cooling by adopting a salt heat exchanger, the molten salt circulation quantity between the first salt bath and the salt heat exchanger is regulated and controlled by a group of molten salt circulation pumps, the molten salt liquid level of the first salt bath is maintained to be 200-500 mm, the molten salt circulation quantity of the first salt bath is 1000t/h, the molten salt temperature in the first salt bath is maintained to be less than or equal to 15 ℃, the end roller way speed of the first salt bath is controlled to be 0.3m/s, and the wire rod is quenched to be the mixed structure of bainite and residual austenite at the bainite transformation temperature.
The second salt bath tank is internally provided with molten salt at 540 ℃, the online salt bath tempering procedure is used for quickly heating the wire rod subjected to online salt bath quenching to the molten salt temperature for high-temperature tempering when the wire rod is subjected to the second salt bath tank, namely, the salt bath tempering temperature is controlled to be 540 ℃, the salt bath tempering time is controlled to be 339s, the quenched and heated molten salt is quickly subjected to heat exchange and cooling by adopting a salt heat exchanger, a group of molten salt circulating pumps are used for regulating and controlling the circulating amount of the molten salt between the second salt bath tank and the salt heat exchanger, the liquid level of the molten salt in the second salt bath tank is maintained to be 200-400 mm, maintaining the temperature rise of molten salt in the second salt bath at less than or equal to 10 ℃, increasing the initial roller way speed of the second salt bath to 0.8m/s, reducing the roller way speed of the wire rod to 0.3m/s after the wire rod passes through the second salt bath for 20s, adjusting the temperature difference of the wire rod lap joint area and the non-lap joint area to less than or equal to 10 ℃, converting bainite in the wire rod into tempered bainite, converting residual austenite into ferrite and pearlite structures, cleaning, air cooling and collecting the wire rod discharged from the second salt bath, and then carrying out off-line transportation, packaging and warehousing to obtain a finished spring steel wire rod, wherein the metallographic structure diagram of the finished spring steel wire rod is shown in figure 3.
Comparative example 2:
The production process of the spring steel wire rod is different from the embodiment 2 in that: the salt bath quenching temperature of the online salt bath quenching process is 285 ℃, and the salt bath quenching time is 40s, so that the spring steel wire rod is obtained.
Example 3:
The invention relates to a production process of a hot-rolled chromium-free low-strength high-plasticity spring steel wire rod, which comprises the following chemical components in percentage by mass: c:0.57%, si:1.32%, mn:0.64%, P:0.008%, S:0.01% of Fe and the balance of unavoidable impurities; the production process comprises the steps of hot rolling, spinning, on-line salt bath quenching and on-line salt bath tempering, and specifically comprises the following steps of:
The hot rolling process is used for rolling square billets with the chemical components and the specification of 160mm multiplied by 160mm into wires with the diameter of 12mm through a rolling line, the wire laying process is used for rolling the wires subjected to hot rolling into wire rods through a wire laying machine, the wire laying temperature is controlled to be 993 ℃, the wire rods subjected to wire laying are distributed on a roller way in a scattered manner, and the wire rods are sequentially conveyed along a first salt bath and a second salt bath through the roller way.
The online salt bath quenching process is used for quickly reducing the temperature of the wire rod to be the molten salt temperature according to the cooling speed of 44 ℃/s when the wire rod passes through the first salt bath after spinning, namely, the salt bath quenching temperature is controlled to be 347 ℃, the salt bath quenching time is controlled to be 26s, the quenched and warmed molten salt is quickly subjected to heat exchange and cooling by adopting a salt heat exchanger, the molten salt circulation quantity between the first salt bath and the salt heat exchanger is regulated and controlled by a group of molten salt circulation pumps, the molten salt liquid level of the first salt bath is maintained to be 200-500 mm, the molten salt circulation quantity of the first salt bath is 1050t/h, the molten salt temperature in the first salt bath is maintained to be less than or equal to 15 ℃, the end roller way speed of the first salt bath is 0.3m/s, and the wire rod is quenched to be the mixed structure of bainite and residual austenite at the bainite transformation temperature.
The second salt bath tank is internally provided with molten salt at 558 ℃, the online salt bath tempering procedure is used for quickly heating the wire rod subjected to online salt bath quenching to the molten salt temperature for high-temperature tempering when the wire rod is subjected to the second salt bath tank, namely, the salt bath tempering temperature is controlled to be 558 ℃, the salt bath tempering time is controlled to be 374s, the quenched and heated molten salt is quickly heat-exchanged and cooled by adopting a salt heat exchanger, a group of molten salt circulating pumps are used for regulating and controlling the circulating amount of the molten salt between the second salt bath tank and the salt heat exchanger, the liquid level of the molten salt in the second salt bath tank is maintained at 200-400 mm, maintaining the temperature rise of molten salt in the second salt bath at less than or equal to 10 ℃, increasing the initial roller way speed of the second salt bath to 0.8m/s, reducing the roller way speed of the wire rod to 0.3m/s after the wire rod passes through the second salt bath for 20s, adjusting the temperature difference of the wire rod lap joint area and the non-lap joint area to less than or equal to 10 ℃, converting bainite in the wire rod into tempered bainite, converting residual austenite into ferrite and pearlite structures, cleaning, air cooling and collecting the wire rod discharged from the second salt bath, and then carrying out off-line transportation, packaging and warehousing to obtain a finished spring steel wire rod, wherein the metallographic structure diagram of the finished spring steel wire rod is shown in figure 4.
Comparative example 3:
The production process of the spring steel wire rod is different from the embodiment 3 in that: and the salt bath tempering temperature of the online salt bath tempering process is 502 ℃, and the salt bath tempering time is 290s, so that the spring steel wire rod is obtained.
Example 4:
The invention relates to a production process of a hot-rolled chromium-free low-strength high-plasticity spring steel wire rod, which comprises the following chemical components in percentage by mass: c:0.59%, si:1.19%, mn:0.56%, P:0.009%, S:0.01% of Fe and the balance of unavoidable impurities; the production process comprises the steps of hot rolling, spinning, on-line salt bath quenching and on-line salt bath tempering, and specifically comprises the following steps of:
The hot rolling process is used for rolling square billets with the chemical components and the specification of 220mm multiplied by 220mm into wires with the diameter of 14mm through a rolling line, the wire laying process is used for rolling the wires subjected to hot rolling into wire rods through a wire laying machine, the wire laying temperature is controlled to be 962 ℃, the wire rods subjected to wire laying are distributed on a roller way in a scattered manner, and the wire rods are sequentially conveyed along a first salt bath and a second salt bath through the roller way.
The online salt bath quenching process is used for quickly reducing the temperature of the wire rod to be the molten salt temperature according to the cooling speed of 36 ℃/s when the wire rod passes through the first salt bath after spinning, namely, the salt bath quenching temperature is controlled to be 327 ℃, the salt bath quenching time is controlled to be 28s, the quenched and warmed molten salt is quickly subjected to heat exchange and cooling by adopting a salt heat exchanger, the molten salt circulation quantity between the first salt bath and the salt heat exchanger is regulated and controlled by a group of molten salt circulation pumps, the molten salt liquid level of the first salt bath is maintained to be 200-500 mm, the molten salt circulation quantity of the first salt bath is 1200t/h, the molten salt temperature in the first salt bath is maintained to be less than or equal to 15 ℃, the end roller way speed of the first salt bath is 0.3m/s, and the wire rod is quenched to be the mixed structure of bainite and residual austenite at the bainite transformation temperature.
And molten salt at 549 ℃ is arranged in the second salt bath, the online salt bath tempering procedure is used for quickly heating the wire rod subjected to online salt bath quenching to the molten salt temperature for high-temperature tempering when the wire rod passes through the second salt bath, namely, the salt bath tempering temperature is controlled to be 549 ℃, the salt bath tempering time is controlled to be 352s, the quenched and heated molten salt is quickly heat-exchanged and cooled by adopting a salt heat exchanger, a group of molten salt circulating pumps are used for regulating and controlling the molten salt circulation quantity between the second salt bath and the salt heat exchanger, the molten salt liquid level of the second salt bath is maintained at 200-400 mm, the molten salt temperature in the second salt bath is maintained to be less than or equal to 10 ℃, the initial roller speed of the second salt bath is increased to 0.8m/s, the temperature difference of the temperature of the wire rod in the wire rod passing through the second salt bath is controlled to be less than or equal to 10 ℃ and the temperature of the wire rod in the non-lap joint area is controlled to be 0.3m/s, the bainite in the wire rod is converted into tempered bainite, the retained bainite is converted into ferrite and pearlite tissues, the wire rod out of the second salt bath is washed, the wire rod in the second salt bath is cooled, the air-cooled coil is cooled, the coil is cooled, and the coil spring is cooled after the coil is cooled, and the coil spring is stored, and finished, and the coil spring is obtained.
The spring steel wire rods obtained in the above examples and comparative examples were subjected to structure and performance tests: the same circle intensity difference testing method comprises the following steps: taking 2 coils from the end part of the coil, taking the position of a lap joint area as a base point, equally dividing each coil into 8 sections, respectively taking 1 tensile sample on each section, wherein the extremely poor strength of the tensile sample after tensile test is the same coil difference of the coil, and the tensile test adopts the section 1 of the tensile test of GB-T228.1-2021 metal materials: room temperature test method, to obtain tensile strength and reduction of area, the comparative results obtained are shown in table 1 below:
TABLE 1 comparison of the composition of spring steel wire rods with the wire rod structure properties of the production process
Aiming at the problems that the existing hot rolled wire rod is high in matrix strength and low in plasticity of materials under the stelmor wire-controlled cooling process, and drawing fracture is easy to cause, compared with the air-cooled wire rod, the invention adopts C-Si-Mn and chromium-free spring steel component design, combines on-line rapid salt bath quenching and salt bath tempering isothermal technical process design, so that the wire rod is rapidly reduced from the temperature above A3 to the bainite transformation temperature, then isothermal tempering is performed at high temperature, the regulation and control of the quenching and tempering structure of the chromium-free spring steel hot rolled wire rod are realized by utilizing the characteristic of high heat exchange capability of molten salt, the microstructure type is a mixed structure composed of pearlite, a small amount of tempered bainite and ferrite, and further, compared with the air-cooled wire rod, the wire rod strength is lower, the plasticity is obviously increased, no abnormal structures such as martensite, bainite and the like are adopted, the tensile strength is 908-946 MPa, the section shrinkage Z is 63-68%, the invention is used for the application fields of manufacturing high-strength springs and the like, the problems of soft wire rod manufacturing fracture, the high-strength and the ultrahigh-strength and ultrahigh-strength soft wire rod hardness soft wire rod hardening are effectively solved; (2) Compared with an air cooling line, the method does not need to consider the adverse effect of the height Wen Tusi on the structure and the on-line time, so that the abrasion to the rolling line during hot rolling can be further reduced by adopting the height Wen Tusi, and the production rhythm and the efficiency of the spring steel wire rod are higher. (3) Compared with an air cooling line, the temperature difference between the lap joint area and the non-lap joint area of the wire rod can be adjusted by adjusting the roller speed of the wire rod passing through the first salt bath and the second salt bath, the same-circle strength difference of the wire rod can be further reduced, the same-circle strength difference is less than or equal to 25MPa, and compared with a Steyr air cooling wire rod, the wire rod has lower mechanical fluctuation, and the risk of wire breakage during drawing is further reduced.
From the comparison of examples 1 to 4 and the comparison of example 2 and comparative example 2, it is seen that the lower the salt bath quenching temperature and the longer the salt bath quenching time, the more the transformation of bainite is, whereas the tempered bainite content is increased, whereas the tempered bainite content is decreased, and if the salt bath quenching temperature is too low and the salt bath quenching time is too long, the tempered bainite content is too much, the pearlite content is decreased, and the regulation of the target structure is affected, resulting in a significant decrease in the wire rod, particularly in the plasticity.
From the comparison of examples 1 to 4 and the comparison of example 3 and comparative example 3, it is seen that the higher the salt bath tempering temperature and the longer the salt bath tempering time, the higher the content of retained austenite converted into pearlite and the lower the ferrite content, whereas the lower the content of pearlite and the higher the ferrite content were, the insufficient transformation of bainite structure was caused by the too short salt bath tempering time, affecting the regulation of the target structure, and the reduction of wire rod strength and plasticity was caused.
Therefore, the invention can further regulate and control the tissue transformation of the wire rod by controlling the technical parameters of the on-line salt bath quenching and the on-line salt bath tempering, and complete the regulation and control of the quenching and tempering tissue of the spring steel wire rod, thereby regulating and controlling the strong plastic matching of the spring steel wire rod, effectively reducing the risk of drawing broken wires in a wire manufacturing plant and having good industrial adaptability.
The above list of detailed descriptions is only specific to practical embodiments of the present invention, and they are not intended to limit the scope of the present invention, and all equivalent embodiments or modifications that do not depart from the spirit of the present invention should be included in the scope of the present invention.
Claims (10)
1. The hot-rolled chromium-free low-strength high-plasticity spring steel wire rod is characterized by comprising the following chemical components in percentage by mass: c:0.51% -0.59%, si:1.15 to 1.65 percent of Mn:0.55 to 0.85 percent, less than or equal to 0.020 percent of P, less than or equal to 0.015 percent of S, and the balance of Fe and unavoidable impurities; the structure of the spring steel wire rod comprises a mixed structure composed of 10-20% by volume of tempered bainite, less than 20% by volume of ferrite and the balance of pearlite.
2. The hot-rolled chromium-free low-strength high-plasticity spring steel wire rod according to claim 1, wherein the specification of the spring steel wire rod is 6-15mm, the tensile strength Rm is 908-946 MPa, the area shrinkage is 63-68%, and the same-circle strength difference is less than or equal to 25MPa.
3. A production process of a hot-rolled chromium-free low-strength high-plasticity spring steel wire rod is characterized in that a wire rod is produced by hot rolling chemical components of the hot-rolled chromium-free low-strength high-plasticity spring steel wire rod based on the method in claim 1, the wire rod is spun into the wire rod, then passes through a first salt bath, the wire rod is quenched into a mixed structure of bainite and residual austenite at the bainite transformation temperature according to the cooling rate of more than 30 ℃/s, and then passes through a second salt bath for heating and tempering, so that the spring steel wire rod with the mixed structure composed of 10-20% by volume of tempered bainite, less than 20% by volume of ferrite and the balance pearlite is produced.
4. The process for producing a hot rolled chromium-free low strength high plasticity spring steel wire rod according to claim 3, wherein the heat evidence is that the wire laying temperature of the wire laying process is more than 50 ℃ above wire rod A3 point.
5. The process for producing a hot rolled chromium-free low-strength high-plasticity spring steel wire rod according to claim 3, wherein the heat evidence is that the salt bath quenching temperature of the first salt bath is 300-350 ℃ and the salt bath quenching time is 25-35 s.
6. The production process of the hot-rolled chromium-free low-strength high-plasticity spring steel wire rod, which is disclosed in claim 5, wherein the heat evidence is that the molten salt circulation amount of the first salt bath is 1000-1200 t/h, and the temperature rise of the molten salt is less than or equal to 15 ℃.
7. The process for producing hot rolled chromium-free low-strength high-plasticity spring steel wire rods according to claim 3, wherein the heat evidence is that the salt bath tempering temperature of the second salt bath is 530-560 ℃ and the salt bath tempering time is 300-3800 s.
8. The process for producing the hot rolled chromium-free low-strength high-plasticity spring steel wire rod, which is characterized in that the second salt bath adopts circulating molten salt, and the temperature rise of the molten salt is less than or equal to 10 ℃.
9. The production process of the hot rolled chromium-free low-strength high-plasticity spring steel wire rod according to any one of claims 3 to 8, wherein the temperature difference between the lap joint area and the non-lap joint area of the wire rod is not more than 10 ℃ by adjusting the roller speed of the wire rod passing through the first salt bath and the second salt bath.
10. The process for producing hot rolled chromium-free low strength high plasticity spring steel wire rods according to claim 9, wherein the initial roller speed of the second salt bath is higher than the end roller speed of the first salt bath, and the roller speed of the wire rods is reduced after passing through the second salt bath for 20 s.
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